This invention relates to an apparatus for sequentially delivering articles, such as machine parts or components to be assembled in a production process, which are contained in containers, herein referred to as cassettes, designed to hold these articles one above another in evenly spaced tiers such that they can be pushed individually out of the cassette which contains them.
Work stations, for example, of the type disclosed in U.S. Pat. No. 5,219,215, issued Jun. 15, 1993, are well known and extensively used for the production of many kinds of products, and many different kinds of components to be assembled or otherwise worked on are delivered to a designated article-receiving position of such a work station. One of commonly adopted methods of such delivery has been to make use of a container, frequently referred to as a cassette. As shown as an example in FIG. 6, a cassette 90 may be shaped like a box with open front and back sides. Its vertical side walls are provided with tiers of equally spaced horizontally extending guide members 92 such that articles to be delivered or carriers therefor can be supported thereon by their edges and be pushed horizontally backwards out of the cassette by means of a pusher entering the cassette from the front. After a loaded cassette thus structured is placed next to the article-receiving position (or a lifting position), it is lifted tier by tier in a step-wise vertical motion such that the articles contained in tiers inside the cassette can be sequentially pushed out horizontally backward to the article-receiving position.
Many different schemes have been tried for transporting loaded cassettes to a lifting position adjacent to a designated article-receiving position of a work station. According to a very simple method, they are taken one at a time to the lifting position, from which it is moved vertically upward intermittently such that after each of the articles is pushed out, the next article to be pushed out is brought to the same height as the article-receiving position. This method being far from efficient, two cassettes may be placed one on top of the other at the lifting position so that they can be lifted together continuously and sequentially, but the improvement in efficiency by this method is still not significant. Schemes whereby a plurality of loaded cassettes are arranged horizontally next to one another in a row and moved horizontally together to bring them one at a time to the lifting position have also been considered, but none has been very successful for various reasons. Firstly, each cassette, after horizontally moved to the lifting position, must then be moved vertically. This places a severe limitation on the choice of means for horizontal and vertical motions of the cassettes because interference therebetween must be carefully avoided. In view of this problem, an attempt was made to use a screw rod to move a horizontally arranged array of cassettes, but this gave rise to an efficiency problem of another kind. Let us assume that fully loaded cassettes are adapted to be moved from the left to the right on a horizontal path to the lifting position. After each cassette is completely unloaded, it is lowered back to the original height and is pushed away from the lifting position to the right as the next cassette which is fully loaded is brought to the lifting position. After all the cassettes in the row have thus been unloaded, they are on the right-hand side of the lifting position. Motion of the screw rod is then reversed to return all these unloaded cassettes to the left-hand side of the lifting position where the cassettes are reloaded. In other words, reloading of the cassettes must be carried out at exact moments according to an exact time schedule when the unloaded cassettes are returned to the left-hand side of the lifting position. Otherwise, the efficiency of the production process, in which the apparatus is employed, is significantly affected. This places a severe hardship on the operator in charge of the loading.